Process for producing propylene terpolymers

Abstract

The present invention further relates to the propylene terpolymer obtained by said process particularly suitable to be used as films such as cast films, bi- or mono-oriented films and heat-sealable films having good optical properties and excellent sealing properties combined with good shrinkage properties and softness.

What is claimed is: 
     
       1. A process for producing a propylene terpolymer in a single gas-phase polymerization reactor comprising two interconnected polymerization zones comprising the steps of:
 (a) feeding a first gas mixture comprising: 
 (i) a first concentration of propylene; 
 (ii) a first concentration of ethylene; and 
 (iii) a first concentration of a butene;
 into a first interconnected polymerization zone in the presence of a catalyst for producing a polymer; 
 
 (b) directing the polymer into a second interconnected polymerization zone; 
 (c) re-introducing the polymer into the first interconnected polymerization zone; and 
 (d) recovering the propylene terpolymer comprising:
 (i) ethylene derived units; 
 (ii) propylene derived units; and, 
 (iii) butene derived units; 
 wherein the total content of ethylene and butene derived units are present in the propylene terpolymer in an amount not less than 8% by weight, based on the total weight of the propylene terpolymer, 
 wherein the weight ratio of ethylene to butene ranges from 0.21:1 to 0.52:1, 
 wherein when the ethylene content ranges from 2.30 to 3.10% by weight, based on the total weight of the propylene terpolymer, the butene content is higher than 5.9% by weight, based on the total weight of the propylene terpolymer, and 
 wherein the propylene terpolymer comprises 10-13.9 wt. % of a xylene soluble fraction based upon the total weight of the propylene terpolymer and a flexural modulus of less than 750 MPa. 
 
 
     
     
       2. The process of  claim 1 , wherein the first concentration of butene ranges from 7 to 20 mole % based upon the total molar amount of propylene, ethylene and butene present in the first gas mixture. 
     
     
       3. The process of  claim 1 , wherein the catalyst is a Ziegler-Natta catalyst comprising a solid catalyst component wherein the solid catalyst component comprises:
 (i) magnesium chloride; 
 (ii) at least one titanium compound having at least one titanium-halogen bond; and 
 (iii) at least one electron-donor compound; 
 wherein the at least one titanium compound and the at least one electron-donor compound are supported on magnesium chloride. 
 
     
     
       4. The process of  claim 1 , wherein the first concentration of ethylene ranges from 0.5 to 5 mole % based upon the total molar amount of propylene, ethylene and butene present in the first gas mixture. 
     
     
       5. The process of  claim 1 , wherein the propylene terpolymer has a sealing initiation temperature ranging from 100 to 116° C., a fraction soluble in hexane lower than 6 wt % and a melt flow index ranging from 0.1 to 100 g/10 min. 
     
     
       6. A propylene terpolymer film comprising the propylene terpolymer produced in accordance with  claim 1 , wherein said film is characterized by a haze percentage of less than 0.7% and a gloss percentage of greater than 88.5%. 
     
     
       7. The propylene terpolymer film of  claim 6 , wherein said film is characterized by a shrinkage percentage of greater than 30% at a temperature of 110° C. 
     
     
       8. The propylene terpolymer film of  claim 6 , wherein said film is characterized by a flexural modulus value in a range of 500 to 700 MPa. 
     
     
       9. The process of  claim 1 , wherein the first interconnected polymerization zone is a riser and the second interconnected polymerization zone is a downcomer.